present invention relates to a cooling system for an internal-combustion engine of a motor vehicle comprising a radiator and a thermostatic valve which controls a flow of a coolant between the internal-combustion engine and the radiator in such a manner that, during a warm-up phase, the coolant coming from the internal-combustion engine flows back to the internal-combustion engine while bypassing the radiator through a short circuit. During an operating phase in a mixed operating mode, the coolant coming from the internal-combustion engine flows partially through the radiator and partially through the short circuit back to the combustion engine. In a further operating phase, in a cooling operating mode, the coolant coming from the internal-combustion engine flows back to the internal-combustion engine essentially through the radiator. The thermostatic valve, whose working range is fixed for the mixed operating mode to a predetermined temperature by the design of the expansion element, contains an electrically heatable expansion material. This material enlarges the opening cross-section in comparison to a position caused by the temperature of the coolant and can be supplied with electric energy by means of a control which receives the operating data of the internal-combustion engine and which, as a function of these operating data, controls the supply of electric energy to the expansion element in order to shift the working range of the thermostatic valve from the mixed operating mode to the cooling operating mode and back.
In a cooling system shown in German Patent Document DE 30 18 682 A1, an electric heating resistor is arranged in an expansion element of a thermostatic valve. This electric heating resistor can be supplied with electric energy through a stationarily held working piston. The supply of the electric energy takes place via a control device in order to keep the coolant temperature controlled by the thermostatic valve constant to a degree that is improved with respect to a normal thermostatic valve; i.e., in order to make a correction and shorten the control intervals. For this purpose, the actual coolant temperature is measured and is compared with a predetermined upper temperature valve and with a predetermined lower temperature value. When the upper temperature value is reached, the heating resistor is supplied with electric energy so that the thermostatic valve opens up more in order to obtain an increased cooling output and thus a lowering of the actual coolant temperature. When the actual coolant temperature falls below the lower temperature value, the supply of electric energy to the heating resistor is interrupted so that the expansion element is cooled by the colder coolant. As a result, the valve cross-section is reduced again so that the actual coolant temperature will rise again. These control cycles are repeated constantly in order to maintain a coolant temperature of, for example, 95.degree. C. as constant as possible.
It is known from German Patent Document DE 37 05 232 A1 to provide, instead of a conventional thermostatic valve with an expansion element, a valve which can be controlled by means of a servomotor. In an embodiment, the servomotor is a thermostatic working element whose housing is stationarily arranged outside the valve housing. Inside the valve housing, a valve body is disposed which carries a main valve disk and a short-circuit valve disk in the arrangement known in the case of thermostatic valves. The working piston of the thermostatic working element serving as the servomotor is connected with the valve body. The housing of this thermostatic working element extends transversely with respect to a coolant pipe which leads back to the engine and extends around the valve housing. The housing of the working element projects out of this pipe and is surrounded in this area by a heating element. A control device, to which individual characteristic-diagram quantities are supplied which are sensed, for example, by sensors of the internal-combustion engine, is assigned to this heating device. In addition to the coolant temperature sensed in a forward flow pipe, the exhaust gas temperature and/or the rotational speed and/or the torque of the internal-combustion engine and/or the vacuum in the suction pipe and/or a pressure difference in a vacuum box and/or the oil temperature, or the like, are to be sensed as characteristic-diagram quantities.
In German Patent Application P 42 33 913.8, which is not a prior publication, an electrically heatable thermostatic valve for a coolant circulating system of an internal-combustion engine is disclosed. In the case of this thermostatic valve, the housing of the expansion element is held in a stationary manner by means of its end opposite a working piston and is provided with an electric heating element. The working piston is provided with a short-circuit valve disk and a main valve disk which is pot-shaped and surrounds the housing of the expansion element in a cage-like manner and to which a valve seat is assigned and is sealed off by an additional sealing point with respect to the housing of the expansion element or a holding device surrounding it. As a result of the supply of electric energy to the heating element, an additional control variable can be superimposed on the conventional coolant-temperature-dependent control of the thermostatic valve by means of which variable the main valve is opened more.
It is an object of the present invention to provide for a cooling system of the initially described type a control which is constructed to be as simple as possible, which, on the one hand, permits a lowering of the fuel consumption and an improvement of the exhaust gas composition but which, on the other hand, does not impair the operational reliability and the power output of the internal-combustion engine.
In a cooling system of the initially described type, this object is achieved in that the control comprises at least three comparison stages which are connected in parallel, which each compare an actual value with a predetermined value and, when this predetermined value is exceeded, open up the supply of electric energy to the expansion element. These comparison stages are constructed as a speed comparison stage which compares the actual speed of the vehicle with a predetermined speed value; a load-condition comparison stage which compares the actual load condition of the internal-combustion engine with a predetermined load condition value; and an intake air temperature comparison stage which compares the actual temperature of the air taken in by the internal-combustion engine with a predetermined temperature value.
As a result of the operation of the thermostatic valve, which is a function of the temperature of the coolant, a high coolant temperature and therefore a high engine temperature can be set while, at the same time, depending on the demand, a respective increased cooling output is made available by means of the control. As a result of the increased engine temperature, frictions, for example, are reduced so that the power consumption of the internal-combustion engine is lower. The fuel consumption can therefore be lowered while the exhaust gas composition is improved at the same time. The comparison stages provide that, when an increased cooling output is desired, a switching takes place to a lower temperature level. By means of the speed comparison stage, up to defined standard speeds, the consumption is minimized and the exhaust gas composition is improved. By means of the load condition comparison stage, which, starting at a predetermined load condition, supplies electric energy to the heating device of the expansion element, it is ensured that the power output of the internal-combustion engine is not reduced by an excessive operating temperature which could lead to an impaired volumetric efficiency and thus to a reduced power output. By means of the intake air temperature comparison stage, it is ensured that, for example, during a slow drive or in a traffic jam, the intake air temperature does not rise so much that, even when the power of the internal-combustion engine is relatively low, an insufficient fuel mixture is fed by which the operation of the internal-combustion engine may be disturbed. The three comparison stages therefore lead to a relatively simple control which, in an advantageous manner, takes into account the most important operating conditions of the internal-combustion engine of the vehicle and provides a cooling which in each case depends on the demand.
In certain embodiments of the invention, the control comprises a coolant temperature comparison stage which compares the actual temperature of the coolant with a desired temperature and, when the values of the actual temperature are below the desired temperature, blocks the feeding of electric energy to the expansion element. Thus, it is ensured that a control of the coolant temperature in the direction of a reduced temperature level will be carried out only when a minimum temperature, that is, the desired temperature, is already reached.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.